In the case of a legal separation, Illinois law allows that any person living separate and apart from his or her spouse without fault may have remedy for reasonable support and maintenance while living apart. The action would be brought in the circuit court of the county in which the respondent resides, or in which the parties last resided together as husband and wife. If the respondent cannot be located in Illinois, the action may be brought in the circuit court in the county in which the petitioner resides. Commencement of action, temporary relief, and trials shall be the same as in actions for dissolution of marriage.
A legal separation will not completely terminate your marital status. In order to do so you must seek a dissolution or a declaration of invalidity of marriage (annulment).